Image forming apparatus

ABSTRACT

An image forming apparatus includes: an image forming section that forms a toner image on a sheet; a fixing section that fixes the toner image on the sheet; a sheet conveyance path that branches into a first sheet conveyance path and a second sheet conveyance path downstream of the fixing section; a blowing section that guides the sheet to the first sheet conveyance path or to the second sheet conveyance path by blowing air to the sheet; and a controller that controls the blowing air of the blowing section.

This application is based on Japanese Patent Application No. 2008-130550filed on May 19, 2008, which is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an advancing direction switchingsection for a sheet that is in a sheet conveyance path of an imageforming apparatus.

In general, an image forming apparatus of an electrophotographic typetransfers a toner image visualized through toner development onto asheet, and fixes the toner image on a sheet by pressing and heating thesheet onto which the toner image has been transferred with a fixingsection.

The aforesaid sheet which has been subjected to fixing processing by theaforesaid fixing section is guided to the first sheet conveyance path orto the second sheet conveyance path, by a sheet conveyance pathswitching section that switches advancing directions for a sheet.

The aforesaid first sheet conveyance path is, for example, a sheetconveyance path through which the aforesaid sheet is sent to a sheetejection tray of the image forming apparatus, or to a sheet finisherthat is connected to the downstream side, while, the aforesaid secondsheet conveyance path is, for example, a sheet conveyance path throughwhich the aforesaid sheet is sent to a sheet reversing device, or to asheet re-feeding device that is for forming an image on the reverse sideof the aforesaid sheet.

Many of the aforesaid sheet conveyance path switching sections areconstructed so that the aforesaid sheet may be guided to the prescribedsheet conveyance path by moving the sheet guide member on which aleading edge portion of the sheet rubs, and therefore by regulating theadvancing direction of the sheet (for example, see Unexamined JapanesePatent Application Publication No. 2006-330250).

The sheet conveyance path switching section of this kind can be realizedin a simple structure, and it is characterized to be low in cost, but itgives strong stress to the sheet, because the sheet immediately afterfixing processing comes in pressure contact with a guide member to bebent.

Further, there are sometimes caused problems wherein toner and wax onthe sheet surface stick to the aforesaid sheet guide member, and thesticking toner and wax stick again to the sheet because an image surfaceof the sheet heated by fixing processing rubs against the sheet guidemember.

SUMMARY OF THE INVENTION

The invention has been achieved in view of the situations mentionedabove, and its object is to realize an image forming apparatus having asheet conveyance path that branches into the first sheet conveyance pathand the second sheet conveyance path at the downstream side of a fixingunit, wherein there is provided an air sending section that switches thesheet conveyance path for the sheet to the first conveyance path or tothe second conveyance path, by blowing air against the sheet.

An aspect for attaining the aforesaid object is as follows.

An image forming apparatus characterized in that an image formingsection that forms a toner image on a sheet, a fixing section that fixesthe toner image on the sheet, a sheet conveyance path that branches intothe first sheet conveyance path and the second sheet conveyance path atthe downstream side of the aforesaid fixing section, a blowing sectionthat guides the aforesaid sheet to the first sheet conveyance path or tothe second sheet conveyance path by blowing air to the sheet and acontroller that controls blowing of the blowing section, are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of a conventional image formingapparatus.

FIG. 2 is a conceptual diagram of an image forming apparatus in thepresent embodiment.

FIG. 3 is a block diagram showing relationship for controlling an imageforming apparatus.

FIG. 4 is a diagram illustrating relationship of arrangement for a sheetconveyance path and a blowing member.

FIG. 5 is a block diagram illustrating the structure of the blowingsection.

Each of FIGS. 6( a)-6(d) shows an example of an air amount changingsection.

FIG. 7 is a flow chart showing a flow of blowing control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of the embodiment of the invention will be explained asfollows based on drawings. Incidentally, the invention is not limited tothe present example.

FIG. 1 is a conceptual diagram of a conventional color image formingapparatus G.

The color image forming apparatus G exemplified in the drawing is onethat is called a tandem type color image forming apparatus wherein aplurality of photoconductors 31Y, 31M, 31C and 31K are arranged intandem to face a single intermediate transfer belt 41, and a full-colorimage is formed.

This color image forming apparatus G is equipped, on its upper portion,with automatic document feeder ADF.

Documents D placed on document table 103 of the automatic documentfeeder ADF are separated to be a single sheet to be sent out to adocument conveyance path, and is conveyed by conveyance drum 108.

An image of the documents D during conveyance is read by documentreading section 1 at document image reading position RP. The document Dwhich has been finished in terms of image reading is ejected to documentejection tray 107 by a plurality of conveyance guides and by documentejection roller 105.

Image forming apparatus G is composed of document reading section 1,exposure sections 2Y, 2M, 2C and 2K, image forming sections 3Y, 3M, 3Cand 3K, intermediate transfer section 4, fixing section 5, reversingsheet ejection section 6, sheet re-feeding section 7, sheet feedingsection 8 and control section C which are housed in a single casing.

The document reading section 1 illuminates a document image with lamp Lat document image reading position RP, and guides its reflected lightwith first mirror unit 11, second mirror units 12, and lens 13, to causethe reflected light to form an image on a light-receiving surface ofcharge coupled device image sensor CCD.

Image signals obtained through photoelectric conversion by chargecoupled device image sensor CCD undergo processes including A/Dconversion by image reading control section 14, shading correction, andcompression, which are stored in a memory of control section C as imagedata.

The aforesaid image data stored in the memory undergo appropriate imageprocessing based on conditions established by a user, and output imagedata are created.

Each of exposure sections 2Y, 2M, 2C and 2K is composed of a laser lightsource, a polygon mirror and a plurality of lenses, and it creates alaser beam.

Each of exposure sections 2Y, 2M, 2C and 2K conducts scanning exposureby a laser beam on the surface of each of photoconductors 31Y, 31M, 31Cand 31K representing constituent elements for image forming sections 3Y,3M, 3C and 3K, corresponding to output information outputted based onthe aforesaid output image data.

A latent image is formed on each of the photoconductors 31Y, 31M, 31Cand 31K through the aforesaid scanning exposure by a laser beam.

Image forming section 3Y is composed of photoconductor 31Y, and of maincharging section 32Y, developing section 33Y, first transfer roller 34Yand cleaning section 35Y which are arranged around the photoconductor31Y. The same is equally true of the photoconductors 31M, 31C and 31K.

Latent images on the photoconductors 31Y, 31M, 31C and 31K are developedby respective developing sections 33Y, 33M, 33C and 33K which correspondto the aforesaid photoconductors, whereby, each toner image is formed oneach photoconductor.

The aforesaid toner images formed respectively on photoconductors 31Y,31M, 31C and 31K are transferred one after another at prescribedpositions on intermediate transfer belt 41 representing an intermediatetransfer body, by first transfer rollers 34Y, 34M, 34C and 34K ofintermediate transfer device 4.

Toner remaining on a surface of the photoconductor from which a tonerimage has been transferred is removed by each of cleaning sections 35Y,35M, 35C and 35K.

On the other hand, the aforesaid toner image transferred onto theaforesaid intermediate transfer belt 41 is conveyed by second transferroller 42 from each of trays PG1, PG2 and PG3 of sheet feeding section8, or from sheet feeding device S1, and is transferred onto sheet P thatis fed out after its timing is controlled by sheet feeding roller 81.

A surface of the intermediate transfer belt 41 on which the transfer ofa toner image onto sheet P has been finished is cleaned by belt cleaningsection 43, to be ready for the succeeding image transfer.

On the other hand, sheet P carrying a toner image is conveyed to fixingsection 5 where the toner image is fixed on the sheet P when it ispressed and heated.

Sheet P that has been finished in terms of fixing processing by fixingsection 5 is guided by sheet conveyance path switching section 6 interms of its advance path, and is ejected to sheet ejection tray 61.

When ejecting sheet P after reversing inside out, the sheet P is guideddownward temporarily by sheet ejection guide 62, then, the sheet P isreversed after causing sheet ejection reversing roller 63 to interpose atrailing edge of sheet P, and the sheet is guided to sheet ejectionroller 64 by sheet ejection guide 62 to be ejected.

Incidentally, when forming an image also on the reverse of sheet P,sheet P that is finished in terms of image fixing on the obverse isconveyed to sheet re-feeding section 7 located below by sheet guidemember 62, and the sheet P is reversed by sending it reversely aftercausing re-feed reversing roller 71 to interpose a trailing edge, thus,the sheet P is fed out to sheet re-feeding conveyance path 72 to beready for image forming on the reverse.

FIG. 2 is a conceptual diagram of image forming apparatus G1 in thepresent embodiment.

Though the image forming apparatus G1 is different from color imageforming apparatus G in terms of a structure of sheet conveyanceswitching section 6 at downstream side of a fixing section, other pointsare the same. Thus, the overall explanation will be omitted.

FIG. 3 is a block diagram showing relationship for controlling imageforming apparatus G1.

Control section C1 of image forming apparatus G1 is a computer systemhaving therein CPU, memory M1, an operation unit, I/O port, an interfacefor communication and drive circuit.

The control by the control section C1 is carried out by performing theprescribed programs stored in memory M1.

Further, the control section C1 is connected to a network to be capableof exchanging information with other information exchange equipment.

In the present drawing, meanwhile, descriptions of blocks which are notrelated directly to the explanation of the present embodiment areomitted.

FIG. 4 is a diagram illustrating relationship of arrangement for sheetconveyance path 100 and blowing members 210 and 220.

The sheet conveyance path 100 is one arranged at the downstream side offixing section 5, and it is a sheet conveyance path through which sheetP that has been finished in terms of fixing processing and has beendetected by sheet detection sensor SP in terms of its leading edge isguided to the first sheet conveyance path 101 or to the second sheetconveyance path 102.

At a point where the aforesaid sheet conveyance path 100 is branchedinto the first sheet conveyance path 101 and to the second sheetconveyance path 102, there are arranged first blowing member 210 andsecond blowing member 220 both representing a blowing nozzle that blowsair against sheet P, in a way to face each other.

Meanwhile, in an example shown in FIG. 2, a conveyance path forconveying sheet P toward sheet ejection tray 61 corresponds to the firstsheet conveyance path, and a conveyance path for conveying sheet Ptoward sheet ejection reversing roller (also referred to as sheetreversing section) 63 or toward sheet re-feeding section 7 correspondsto the second sheet conveyance path.

Furthers with respect to a direction of the blowing nozzle, it is notperpendicular to a plane of sheet P, but it is oblique so that a tip ofthe nozzle may be in the advancing direction of sheet P as shown in thedrawing. By providing the inclination of this kind, air can flow in theadvancing direction of sheet P, and conveyance of the sheet isstabilized.

Further, the first blowing member and the second blowing member arearranged so that blown air blowing out of the first blowing member andthe second blowing member may advance in the direction toward theleading edge of the sheet after hitting the surface of the advancingsheet.

FIG. 5 is a block diagram illustrating the structure of blowing section200.

The blowing section 200 is composed of first blowing member 210, airvalve 211, second blowing member 220, air valve 221, air tank 230, airpump 240 and air duct 260.

The air pump 240 sends air so that air pressure in the air tank 230 maykeep prescribed pressure.

Air in the aforesaid air tank is sent to the first blowing member 210 orto the second blowing member 220, when air valve 211 or air valve 212which is opened or closed by instruction signals 219 or 229 of controlsection C1 is opened. Further, air sending to the first blowing member210 or to the second blowing member 220 is intercepted, when the airvalve 211 or the air valve 212 is closed.

Owing to the structure mentioned above, timing of the start of airblowing from the first blowing member 210 or the second blowing member220, or timing of interception, is controlled by control section C1.

On apical portions respectively of the first blowing member 210 and thesecond blowing member 220, there are respectively provided the first airamount changing section 251 whose position is changed by instructionsignal 218 of control section C1 and the second air amount changingsection 252 whose position is changed by instruction signal 228 ofcontrol section C1.

Namely, an amount of air blowing against sheet P from forefronts of thefirst blowing member 210 and the second blowing member 220 per unit timeis controlled when the control section C1 controls the first air amountchanging section 251 and the second air amount changing section 252.

Each of FIGS. 6( a)-6(d) shows an example of an air amount changingsection. Meanwhile, the structure of the first air amount changingsection 251 is the same as that of the second air amount changingsection 252.

FIG. 6( a) is a conceptual diagram of the first blowing member 210, andair that is conveyed through air duct 260 blows out in the direction ofarrow “f” from slit-shaped air blowing outlet 259 of the first blowingmember 210.

The first air amount changing section 251 is provided on the blowingoutlet of the first blowing member 210. Each of FIGS. 6( b), 6(c) and6(d) is an example of the first are amount changing section 251.

FIG. 6( b) is an example wherein an amount of air that hits sheet P ischanged when member 255 having small holes formed in a staggered patternis moved to a blowing outlet of the first blowing member 210.

Further, FIG. 6( c) is an example wherein an amount of air that hitssheet P is changed when indented member 256 is moved at a blowing outletof the first blowing member 210.

Further, FIG. 6( d) is an example wherein an amount of air that hitssheet P is changed when member 257 that is opened and closedsymmetrically is caused to open and close at a blowing outlet of thefirst blowing member 210.

Each of the aforesaid members 255, 256 and 257 is called an opening areaadjusting member.

FIG. 7 is a flow chart showing a flow of blowing control.

Control of blowing is one wherein sheet P advancing to sheet conveyancepath 100 is guided to the first sheet conveyance path 101 or to thesecond sheet conveyance path 102 by spraying air against sheet Pfollowing specifications of a job established in advance, and sheet Pthat advances further receives blowing to cool an image plane.

After the leading edge of sheet P is detected by sheet detection sensorSP (step S1: Y), sheet conveyance path selection information that isdetermined by specifications of the job established on image formingapparatus G1 is acquired. Further, sheet leading edge positioninformation that is a distance by which the leading edge of sheet Padvances from a position of the sheet detection sensor SP is calculatedone after another from a conveyance speed of sheet P (step S2).

After it becomes clear that the leading edge of sheet P has arrived atthe position established in advance by the aforesaid calculated sheetleading edge position information (step S3: Y), the sheet P is judgedwhether it is sheet P to be sent to the first sheet conveyance path 101or not, referring to the aforesaid acquired sheet conveyance pathselection information (step S4).

If the sheet P is one to be sent to the first sheet conveyance path,second air valve 212 is opened so that air may blow out of secondblowing member 220 positioned below the sheet P (step S5). An amount ofair blowing out per unit time is determined by the second air amountchanging section 252.

When a leading edge portion of sheet P is guided to the first sheetconveyance path 101 by air blowing out of the second blowing member 220and the leading edge of sheet P arrives at an air amount changingposition established in advance (step 6: Y), an amount of air blowingout of the second blowing member 220 is reduced (step S7).

A change of an amount of air blowing out of the second blowing member220 of this kind reduces problems that contact between an image surfaceof sheet P and a sheet guide member of the first sheet conveyance pathis weakened, toner and wax on the sheet surface stick to the aforesaidsheet guide member.

Meanwhile, in the example stated above, a leading edge portion of sheetP is guided by air blowing out of the second blowing member 220 to thefirst sheet conveyance path 101, for easy understanding of theexplanation. However, it is preferable to construct so that air may blowout of both the first blowing member 210 and the second blowing member220, and a leading edge portion of sheet P may be guided to the firstsheet conveyance path 101 by the difference between an amount of airfrom the first blowing member 210 and that of air from the secondblowing member 220.

By constituting as stated above so that both sides of sheet P areconstantly hit by air, air flows constantly on an image surface of sheetP, thus, a toner image heated in fixing device 5 is cooled rapidly,rubbing between sheet P and a sheet guide member is reduced, and aproblem that toner and wax on the surface of the sheet stick to thesheet guide member is further reduced.

After the trailing edge of sheet P is detected by sheet detection sensorSP (step S8: Y), or after the passage of prescribed time since thedetection, an air valve that has been opened is closed (step 12) tofinish the routine.

On the other hand, in step S4, when sending sheet P to second sheetconveyance path 102 (step S4: N), the first air valve 211 is opened(step S9) so that air may blow out of the first blowing member 210 thatis located above the sheet P. Meanwhile, an amount of air emitted perunit of time is determined by the first air amount changing section 251.

When a leading edge portion of sheet P is guided to the second sheetconveyance path 102 by air blowing out of the first blowing member 210and the leading edge arrives at a position for changing an amount of airestablished in advance (step S10: Y), an amount of air blowing out ofthe first blowing member 210 is reduced (step S11).

In the example stated above again, a leading edge portion of sheet P isguided by air blowing out of the second blowing member 210 to the secondsheet conveyance path 102, for easy understanding of the explanation.However, it is preferable to construct so that air may blow out of boththe first blowing member 210 and the second blowing member 220, and aleading edge portion of sheet P is guided to the second sheet conveyancepath 102 by the difference between an amount of air from the firstblowing member 210 and that of air from the second blowing member 220.

By constituting, as stated earlier, so that both sides of sheet P may beconstantly hit by air, air flows constantly on an image surface of sheetP, thus, a toner image heated in fixing device 5 and sheet P are cooledrapidly, and rubbing between sheet P and a sheet guide member isreduced.

As a result, a problem that toner and wax on a surface of the sheetstick to the sheet guide member, and a problem of occurrence of curlswhich are caused when strong stress is applied on overheated sheet P,are reduced.

After the trailing edge of sheet P is detected by sheet detection sensorSP (step S8: Y), or after the passage of prescribed time since thedetection, an air valve that has been opened is closed (step 12) tofinish the routine.

In the case of switching of sheet conveyance paths in the presentembodiment in the image forming apparatus having a sheet conveyance paththat is branched into the first sheet conveyance path and the secondsheet conveyance path, at the downstream side of the fixing device,occurrence of curls of sheets can be suppressed, because strong stressis not applied on the sheet immediately after fixing processing, whichis different from sheet conveyance path switching in which a sheetconveyance path is switched by a sheet guide member.

Further, it is possible to prevent a problem that toner and wax stick tothe sheet guide member and to stick again to the sheet, because an imagesurface of the sheet heated by fixing processing does not rub stronglyagainst the aforesaid sheet guide member, and is further cooled by air.

1. An image forming apparatus comprising: (a) an image forming sectionthat forms a toner image on a sheet; (b) a fixing section that fixes thetoner image on the sheet; (c) a sheet conveyance path that branches intoa first sheet conveyance path and a second sheet conveyance pathdownstream of the fixing section; (d) a blowing section that guides thesheet to the first sheet conveyance path or to the second sheetconveyance path by blowing air to the sheet; and (e) a controller thatcontrols the blowing air of the blowing section.
 2. The image formingapparatus of claim 1, wherein the blowing section comprises a firstblowing member and a second blowing member which blow air of the blowingsection, wherein the first and second blowing members are arranged toface each other.
 3. The image forming apparatus of claim 2, wherein eachof the first and second blowing members comprises a slit-shaped airblowing outlet.
 4. The image forming apparatus of claim 2, wherein thefirst and second blowing members are arranged so that blown air blowingout each of of the first blowing member and the second blowing memberadvances toward a leading edge of the sheet after hitting a surface ofthe advancing sheet.
 5. The image forming apparatus of claim 2, whereinthe first blowing member comprises a first air amount changing sectionwhich changes an amount of blown air blowing out of the first blowingmember, and the second blowing member comprises a second air amountchanging section which changes an amount of blown air blowing out of thesecond blowing member.
 6. The image forming apparatus of claim 5,wherein each of the first and second air amount changing sectionscomprises an opening area adjusting member which changes an opening areaat the air blowing outlet, and changes the amount of the blown airblowing out of the air blowing outlet by moving the opening areaadjusting member.
 7. The image forming apparatus of claim 2, wherein theblowing section comprises a first air valve which sends or interceptsair blowing from the first blowing member, and a second air valve whichsends or intercepts air blowing from the second blowing member.
 8. Theimage forming apparatus of claim 7, wherein the controller calculatespositional information of a leading edge of the conveyed sheet on thebasis of a signal sent from a sheet detection sensor that detects theleading edge of the sheet, determines a timing of the sending air or theintercepting air on the basis of the calculated positional information,and changes the amount of the air blowing out of each of the first andsecond air amount changing sections.
 9. The image forming apparatus ofclaim 1, further comprising: a sheet ejection tray which receives thesheet ejected from the apparatus; and a re-feeding section through whichthe sheet having an image on a front side thereof is re-fed for formingan image on a rear side, wherein the first sheet conveyance path is aconveyance path through which the sheet is conveyed to the sheetejection tray, and the second sheet conveyance path is a conveyance paththrough which the sheet is conveyed to the re-feeding section.
 10. Theimage forming apparatus of claim 1, further comprising: a sheet ejectiontray which receives the sheet ejected from the apparatus; and a sheetreversing section by which a front and rear sides of the sheet arereversed, wherein the first sheet conveyance path is a conveyance paththrough which the sheet is conveyed to the sheet ejection tray, and thesecond sheet conveyance path is a conveyance path through which thesheet is conveyed to the sheet reversing section.